1) Does the stock regulator regulate at 3 bars as well on WOT or idling or partial throttle? When the fuel pressure is increased, does the AFR become more richer as it is atomize and pressureize into cylinder?

2) Effect on increasing the fuel pressure, does it affect the injector dead time? I can see from the video, the voltage were important too. But im not sure about the increasing the pressure.

3 bar is a typical base fuel pressure for a conventional fuel system with a return line. If you are using a vacuum referenced fuel pressure regulator, the regulator's job is to keep the difference between the fuel pressure and the air pressure in the inlet manifold constant. This is called differential pressure. This happens at idle, WOT or in boost.

1. If you raise the fuel differential fuel pressure then the injector will supply more fuel and hence the AFR will become richer.

2. Yes the fuel pressure will effect the injector deadtime. As we raise fuel pressure it becomes harder to open the injector and hence the deadtime increases.